1. Field of the Invention
The present invention relates to a medical guidewire which may be used, for example, to position a catheter, or a balloon catheter, within the vasculature of the human body.
2. Description of the Prior Art
Percutaneous angioplasty is a therapeutic medical procedure which can increase blood flow through a blood vessel. This procedure may sometimes be used as an alternative to coronary by-pass surgery. An elongated catheter having a deflated balloon at its distal end is guided through the cardiovascular system to the coronary artery of the heart. The balloon is inflated to compress deposits that have accumulated along the inner walls of the coronary artery to thereby widen the artery lumen and increase blood flow.
A known technique for positioning a balloon catheter uses an elongated guidewire which is inserted into a patient and routed through the cardiovascular system. The guidewire progress is viewed on an X-ray imaging screen.
Representative prior art patents which disclose flexible, elongated guidewires are U.S. Pat. No. 4,545,390 to Leary; U.S. Pat. No. 4,538,622 to Samson, et al.; U.S. Pat. No. 3,906,938 to Fleischhacker; U.S. Pat. No. 4,846,186 to Box, et al.; and U.S. Pat. No. 5,259,393 to Corso Jr., et al. The latter two patents, assigned to the same assignee as the present applications, are incorporated herein by reference.
One problem with currently available guidewires occurs when the guidewire is being removed from the vasculature of the human body. The coil may become partially detached from the distal end of the guidewire and begin to unravel as the guidewire is being withdrawn with the result that it is possible for the coil to become separated from the corewire of the guidewire. Numerous techniques have been developed to prevent the detachment of the coil from the corewire including various arrangements in which the coil is spot welded to the corewire at the distal tip of the corewire and at least two or three locations along the periphery of the corewire. However, with a continues relatively tight wound coil it is still possible that the coil may become detached from the corewire at one position along the corewire and the helically wrapped coil tends to unwind with the result that the coil is completely released from the corewire along its entire length.
The present invention is directed toward a medical guidewire which includes an elongated corewire having proximal and distal ends and having a first, uniform diameter, proximal portion and a second, more flexible, reduced diameter distal portion. The guidewire also includes a coiled wire spring having distal and proximal ends and including a distal portion comprised of tightly spaced coil turns and a proximal portion comprised of very loosely spaced coil turns. The coiled wire spring is bonded, for example by welding, to the distal tip of the corewire and is also similarly attached to the uniform diameter portion of the corewire over the entire portion of the coiled wire spring which is comprised of loosely spaced coil turns.
The loosely spaced coil turns are very widely spaced from each other in order to cause the coil wire in the region of the loosely spaced turns to extend along the corewire in a direction approaching being longitudinal with respect to the axis of the corewire. Accordingly, in the event the corewire spring becomes detached from the corewire at the distal tip of the corewire, the coil may then begin to unwind over the tightly wound section of the coil spring, but the very loosely spaced coil turns tend to tighten or clamp down on the corewire and thereby function much as a xe2x80x9cChinese finger gripper.xe2x80x9d This gripping on the corewire prevents further unraveling and total detachment of the wire spring from the corewire. This is an important safety feature which largely resists detachment of the coil spring from the corewire.
In accordance with another aspect of the present invention, the coiled corewire is formed of a wire having a cylindrical cross section of a predetermined diameter and adjacent turns of the loosely spaced coiled turns are spaced apart at least three times the diameter of the wire of the coiled wire spring.
In accordance with still another aspect of the present invention, the adjacent turns of the loosely spaced coiled turns are spaced apart at least about five times the diameter of the wire of the coiled wire spring, or alternatively, the adjacent turns of the loosely spaced coiled turns are spaced apart at least about seven times the diameter of the coiled wire spring.
In accordance with still another aspect of the present invention, the coiled wire spring is formed of a wire having a cylindrical cross section with a predetermined diameter, preferably about 0.0025 of an inch, and in which adjacent turns of the loosely spaced coil are spaced apart at least about 0.0125 of an inch. Alternatively, the adjacent turns of the loosely spaced coil are spaced apart at least about 0.0175 of an inch.
Again, if the distal end of the coiled wire spring becomes detached from the distal end of the corewire and the helically wound coil wire spring begins to unwind from the corewire as the distal end of the wire spring is pulled longitudinally, the very loosely spaced coiled turns which extend in a direction approaching that of being longitudinal to the axis of the corewire, serve the function of locking unto the corewire in a manner somewhat analogous to a xe2x80x9cChinese finger gripperxe2x80x9d to thereby prevent further unraveling of the coiled wire from the corewire. Again, this important safety feature significantly prevents detachment of the coil from the corewire.